The battle for the Republican nomination is turning into a "battle of the
billionaires" as wealthy individuals prepare to put their financial
muscle behind candidates struggling to stay in the race.

Spending by outside groups funded by the rich has already reached about $35 million (£23 million) so far but is set to soar as the race heads to South Carolina on Jan 21 and Florida ten days later.

Sheldon Adelson, a Las Vegas casino mogul, has written a £3.2 million check for his friend Newt Gingrich, the former Speaker of the House. Much of it will be spent on a 27-minute documentary attacking the frontrunner and former private equity chief executive Mitt Romney as a "predatory capitalist".

Foster Friess, the Wyoming-based head of a £10 billion investment management business, will spend £516,000 on television advertising for Rick Santorum in South Carolina alone, after spending £474,000 in Iowa where the former Pennsylvania senator essentially tied for first place.

Jon Huntsman Snr has meanwhile already spent £1.29 million on advertising supporting his son, also Jon Huntsman, who came third in New Hampshire earlier this week but has yet to make an impression on voters in the southern state.

The billionaires' money is channeled through so-called Super-PACS (political action committees) which are legally separate entities from campaigns, even though they are almost always run by prominent supporters, friends or relations of candidates and it is obvious from the content of their advertisements which candidates they support.